1. Field of the Invention
The present invention relates to a liquid crystal display device provided with an orientation divider for dividing the orientation direction of a liquid crystal.
2. Description of the Related Art
FIG. 1 shows a plan diagram of a conventional liquid crystal display device. FIG. 2 shows a sectional diagram taken along line B—B of FIG. 1 and FIG. 3 shows a sectional diagram taken along line D—D of FIG. 1.
In can be seen in FIG. 2 and FIG. 3 that a plurality of drain signal lines 50 and a plurality of gate signal lines 51 intersect each other on a first substrate 10 which is made of an insulating substrate such as glass or quartz, and in the vicinity of each intersection of lines 50 and 51 there are provided a thin-film transistor (hereinafter called TFT). Pixel electrodes 19 made of a transparent conductive film such as ITO (Indium Tin Oxide) are connected to sources 13s of the TFT. The drain signal lines 50 are intersected with the gate signal lines 51 and are overlapped with the pixel electrodes 19.
A storage capacitor electrode line 52 is disposed near the TFT in parallel to the gate signal line 51. The storage capacitor electrode line 52 is made of chromium and makes a storage capacitor for storing electric charges by forming a capacitor with an electrode 53 connected to the source 13s of the TFT through an interlayer insulating film 15. This storage capacitor is disposed to be electrically parallel to a liquid crystal 21 which is also a capacitor in order to suppress the electric charges stored in the liquid crystal 21 by a leak current of the TFT and to keep the stored electric charges.
An opposing electrode 34 on the side of a second substrate 30 is a common electrode which is formed to overlap the plurality of pixel electrodes 19. An orientation control window 36, which is formed by removing the ITO as an opposing electrode material so that one end of letter Y indicated by a dotted line in FIG. 1 is made to have the same forked shape as the other end, is disposed at positions corresponding to the respective pixel electrodes 19.
As can be seen in FIG. 2 and FIG. 3, the interlayer insulating film 15, the drain signal line 50 disposed for each pixel, and a planarization insulating film 17 are sequentially formed on the insulating substrate 10, while the pixel electrode 19 made of ITO is disposed for each pixel on the planarization insulating film 17. The pixel electrode 19 is disposed to overlap with the drain signal line 50. A vertical orientation film 20 for orienting the liquid crystal 21 is further disposed on the pixel electrode 19. A polarizer 41 is disposed on the opposite side of the insulating substrate 10 facing the liquid crystal 21.
A color filter 31 comprising red (R), green (G), and blue (B) for showing such colors and a black matrix for shielding light is disposed on the opposite side of the second substrate 30 facing the liquid crystal 21. A protective film 33 made of a resin is formed on the color filter 31 to protect its surface and the opposing electrode 34, which is made of a transparent conductive film of ITO or the like, is formed on the protective film 33. As described above, the orientation control windows 36 for controlling the orientation of the liquid crystal 21 are formed on the opposing electrode 34. A vertical orientation film 35 which vertically orients the liquid crystal 21 is disposed on the orientation control windows 36. A polarizer 42 is disposed on the opposite side of the second substrate 30 facing the liquid crystal 21. The polarizer 42 and the polarizer 41 are disposed so that their polarization axes intersect at right angles.
The insulating substrate 10 and the second substrate 20 are joined at their peripheries using a sealing adhesive agent (not shown), and a nematic liquid crystal 21 which has a negative anisotropy of dielectric constant is filled in a gap formed to complete a liquid crystal display panel. The orientation control windows 36 formed in the opposing electrode 34 are disposed at two positions for each pixel because the orientation control window 36 shows the forked shape in letter Y in FIG. 3.
The liquid crystal 21 has a negative anisotropy of dielectric constant. Here, the behavior of liquid crystal molecules will be described. In a state that a voltage is not applied to the liquid crystal 21, the liquid crystal molecules between the substrates 10 and 30 are vertically oriented with respect to the substrates 10, 30. Therefore, incident light which is linearly polarized by the polarizer 41 on the side of the TFT substrate 10 is not double refracted in the liquid crystal 21 but shielded by the polarizer 42 on the side of the second substrate 30 to show black. This is called a normally black method.
As shown in FIG. 2, when a voltage is applied to the liquid crystal 21, the major axes of the liquid crystal molecules are oriented in the vertical direction with respect to the electric flux line, but controlled to incline in a plurality of orientation directions with respect to one pixel electrode 19 by the electric flux line produced in a slanting direction at the end of the pixel electrode 19 and the end of the orientation control window 36. The incident light which is linearly polarized by the polarizer 41 becomes an elliptical polarized light upon receiving the double refractory by the liquid crystal 21 which has a negative anisotropy of dielectric constant so to pass through the polarizer 42 and have a transmissivity corresponding to a voltage of the drain signal line.
Thus, when the orientation direction of the liquid crystal is divided into multiple numbers in the pixel, the respective regions have a different viewing angle characteristic so that the viewing angle of the pixels as a whole can be enlarged.
In this specification, a means for dividing the orientation direction of the liquid crystal (orientation divider) is indicated as an orientation divider. In addition to the orientation divider described above, other arts, such as an orientation control slope or division of a rubbing direction into multiple numbers, have been proposed.
In the state that a voltage is applied to the liquid crystal 21, however, the liquid crystal molecules as a continuous body are continuously inclined to allow the passage of light according to an electric field produced at the edge of the orientation control window 36 outside the region of the orientation control window 36 formed on the opposing electrode 34, but, in the region of the orientation control window 36, the liquid crystal molecules remain in the vertically oriented state with respect to the substrates 10, 30, so that the light does not pass through the orientation control window and a light-shielding state is kept.
Even when an orientation divider other than the orientation control window is used, a boundary in the orientation direction of the liquid crystal may exist at any position. Such a boundary in the orientation direction is consistently in a state of shielding the light in a normally black mode type and in a state of allowing the light in a normally white mode type because the orientation does not change even if a voltage is applied to between the electrodes.
As shown in FIG. 1 through FIG. 3, the drain signal lines 50 overlap with the pixel electrodes 19 and made of a light-shielding material such as metal. However, when the drain signal line 50 is disposed between the pixel electrodes 19, the liquid crystal is oriented by a signal voltage applied to the drain signal line 50, which results in degraded display quality.
Therefore, there are disadvantages in the conventional art that an effective display region in the pixel electrode forming region must decreased because of the orientation control windows 36 and the drain signal lines 50, an aperture ratio was heavily degraded, and a bright display could not be obtained.